1. Field of the Invention
This invention relates to photographic optical systems and, more particularly, to an optical system for deflecting the image to obtain a stabilized picture when tracking or following the movement of an object or against accidental motion of the photographic instrument.
2. Description of the Related Art
When taking pictures from a moving vehicle such as a running car or a flying aircraft, vibrations are conveyed to the photographic system and its image is caused to accidentally displace. For a given vibration amplitude, the longer the focal length of the photographic system, the larger the degree of displacement of the image becomes.
Vibration-proof optical systems having the function of stabilizing the photographic system's image have been proposed in, for example, Japanese Patent Publications Nos. Sho 56-34847, 57-7414 and 57-7416 and U.S. Pat. Nos. 3,212,420 and 3,378,326.
In these proposals, the photographic system is provided in part with an optical member arranged to remain spatially stationary against vibrations, and the vertical angle is made to change in relation to the vibration of this optical member so that the image is stabilized.
However, such change of the vertical angle gives rise to a problem that the image plane is inclined away from the film surface. Also, the vertical angle must be changed to suit to the motion of the image. This leads to another problem of response characteristics.
Meanwhile, a concrete driving mechanism for stabilizing the image is disclosed in U.S. Pat. application Ser. No. 896,639. The image-stabilizing method used therein is based on the parallel decentering of a lens unit which constitutes part of the photographic system. Since, according to this method, the image is moved vertically on the film plane in response to decentering, the image displacement due to the tilting of the photographic system can be averted.
In order to achieve good stability of the image, on the other hand, it is required that the responsiveness is sufficiently high. It should be recognized here that this requirement can be fulfilled by reducing the size of the lens unit for decentering, but high grade imagery becomes difficult to preserve since that size reduction generally leads to increase the difficulty of well correcting those of the image aberrations which are produced by the decentering, or the so-called decentering aberrations.
Particularly in the above-cited application Serial No. 896,639, concerning the lens design standpoint, that is, simultaneous fulfillment of both requirements of improving both the compactness of the optical system and the optical performance, this problem is not addressed.